Wireless Handover Optimization

ABSTRACT

Aspects of the present invention relate to improved systems and methods for handing over a UE from a source node to a target node. In some embodiments, the target node receives UL and DL count information directly from the UE being handed over, rather than from the source node or from a core network node.

This application is a continuation of application Ser. No. 12/407,438,filed on Mar. 19, 2009, which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to the field of wireless communicationsystems. More specifically, aspects of the present invention relate tosystems and methods for handing over a user equipment between nodes.

BACKGROUND

In the 3rd Generation Partnership Project (“3GPP”) Long Term Evolution(“LTE”) protocol, a user equipment (UE) connects to the core network vianodes (e.g. e-UTRAN NodeB nodes). Typically, the UE connection ismaintained over a single node. However, as the UE moves geographicallyor other network conditions occur, it may be desirable or necessary totransfer the UE connections from the source node (the node to which theUE is currently connected) to an available target node (i.e., perform ahandover from the source node to the target node).

The UE connection with the source node is typically encrypted and thecipher requires uplink (“UL”) and downlink (“DL”) counts for each dataunit, which comprise sequence numbers and/or a Hyper Frame Numbers(“HFN”). Thus, during a handover the source node must to transfer the ULand DL count values to the target node in order to enable the encryptionfeatures of the target node. In the standard 3GPP LTE protocol, thistransfer is done in one of two ways depending upon the protocols enabledwithin the nodes.

If the nodes are configured to operate according to the S1 ApplicationProtocol (“S1AP”), then the transfer of the UL and DL counts occurs viaa two step process. First, during an eNB Status Transfer, the UL and DLcounts are transmitted from the source node to a Mobile ManagementEntity (“MME”) connected to the core network. Then, during an MME StatusTransfer, the UL and DL counts are transmitted from the MME to thetarget node.

Alternatively, if the nodes are configured to operate according to theX2 Application Protocol (“X2AP”), then the transfer of the UL and DLcounts occurs via a SN Status Transfer. During the SN Status transfer,the UL and DL counts are transmitted directly from the source node tothe target node.

After a source node has sent the UL and DL counts to the target node, itmust cease scheduling UE data (e.g. data received from the UE or dataintended for the UE) so that the UL and DL counts remain accurate whenthey are received by the target node. It can also occur that a UEconnects to a target node (and thus has disconnected from the sourcenode) before the target node has received the UL and DL counts from thesource node. In this situation, the UE cannot send or receive any dataunits via the target node until the target node acquires the UL and DLcounts. Thus, during the handover process there can be an undesirableservice interruption while the UE waits for the UL and DL counts to betransferred between the source and target nodes.

Furthermore, there may be a finite amount of time between when the UEdisconnects from the source node (i.e., the source node stops schedulingUE data) and when the core network is notified that the UE has connectedto the target node. During this time period, any DL data units intendedfor the UE may be sent to the wrong node or lost.

SUMMARY

Aspects of the invention provide improved systems and methods forhanding over a UE from a source node to a target node. In someembodiments, the target node receives the UL and DL count informationfrom the UE rather than other nodes in the network. In some embodiments,the source node continues to schedule UE data during the handoverprocess and forwards the scheduled UE data to the target node to ensureall UE data is received.

Thus in one aspect, the invention provides an improved method performedby a source node for handing over a UE from a source node to a targetnode. In some embodiments, the improved method performed by the sourcenode includes: (a) transmitting from the source node to another node afirst handover message that indicates that the UE requires a handover;(b) receiving at the source node a second handover message transmittedfrom the another node in response to the first handover message; (c) inresponse to receiving the second handover message, transmitting from thesource node a reconfiguration message to the UE; (d) after transmittingthe reconfiguration message from the source node to the UE, continuingto schedule the UE in the source node until a particular message isreceived at the source node; and (e) after performing step (d),receiving at the source node a context release message transmitted fromthe another node indicating that the UE has been handed over to thetarget node.

In some embodiments, the another node is the target node. In suchembodiments, the first handover message may be an X2AP Handover Requestmessage, the second handover message may be an X2AP Handover RequestAcknowledge message, and the context release message may be an X2AP UEContext Release message. In addition, the particular message may be anend marker transmitted from a gateway.

In some embodiments, the another node is an MME. In such embodiments,the first handover message may be an S1AP Handover Required message, thesecond handover message may be an S1AP Handover Command message, and thecontext release message may be an S1AP UE Context Release Commandmessage. Additionally, the particular message may be the S1AP UE ContextRelease Command message In some embodiments, the improved method furthercomprises transmitting from the source node to the MME an S1AP UEContext Release Complete message in response to the S1AP UE ContextRelease Command message.

In some embodiments, the source node is configured such that the sourcenode does not transmit to the MME a status transfer message in responseto receiving the S1AP Handover Command message from the MME.

In some embodiments, the method further comprises a step of: (f)transmitting UE data from the source node to the target node aftertransmitting the reconfiguration message to the UE, wherein the UE datacomprises data received from the UE or data intended for the UE.

In some embodiments, the method further comprises a step of: (f) aftertransmitting the reconfiguration message from the source node to the UE,continuing to (i) assign sequence numbers to DL data units intended forthe UE and (ii) deliver data units received from the UE to a corenetwork node until the particular message is received at the sourcenode.

In another aspect, the invention provides a method performed by a UE. Insome embodiments, the method includes the following steps: (a)establishing a connection with a source node; (b) after establishing theconnection, transmitting data units to and receiving data units from thesource node; (c) after step (b), receiving from the source node areconfiguration message identifying a target node; and (d) afterreceiving the reconfiguration message, transmitting to the target node amessage (e.g. a reconfiguration complete message) comprising a DL countvalue and an UL count value.

In some embodiments, the DL count value comprises (1) a sequence numberand/or (2) a HFN that the target node should assign to a DL data unitthat does not have a sequence number assigned to it and that is intendedfor the UE; and the UL count value comprises (1) a sequence numberand/or (2) a HFN.

In some embodiments, the method further comprises the steps of: (e)after receiving the reconfiguration message, receiving a resourceallocation from the source node; and (f) using the allocated resourcesto transmit a data unit to the target node.

In another aspect, the invention provides a method performed by a targetnode. In some embodiments, the method includes the following steps: (a)receiving at the target node a handover request message transmitted fromanother node; (b) transmitting to the another node a handoveracknowledge message in response to the handover request message; (c)after transmitting the handover acknowledge message and beforescheduling the UE in the target node, receiving at the target node amessage transmitted from the UE comprising a DL count value and a ULcount value; and (d) after receiving the message from the UE, using theDL count value and/or the UL count value in a communication with the UE.

In some embodiments, the message transmitted from the UE is areconfiguration complete message that was transmitted by the UE to thetarget node in response to a reconfiguration message transmitted to theUE from the source node.

In some embodiments, the DL count value comprises (1) a sequence numberand/or (2) a HFN that the target node should assign to a DL data unitthat does not have a sequence number assigned to it and that is intendedfor the UE, and the UL count value comprises (1) a sequence numberand/or (2) a HFN.

In some embodiments, the method further comprises: receiving from thesource node a DL data unit for the UE, and determining whether the DLdata unit should be transmitted to the UE, wherein the determination isbased on the DL count value received from the UE.

In another aspect, the invention provides an improved access point(e.g., base station or other access point). In some embodiments, theimproved access point includes: (a) a first receiver for receiving datatransmitted from a user equipment (UE); (b) a first transmitter fortransmitting data to the UE; (c) a second transmitter for transmittingdata to a node; (e) a second receiver for receiving data from the node;and (f) a data processing system operable to: (i) transmit to the node afirst handover message that indicates that the UE requires a handover;(ii) receive a second handover message transmitted from the node inresponse to the first handover message; (iii) transmit a reconfigurationmessage to the UE in response to receiving the second handover message;(iv) continue to schedule the UE after transmitting the reconfigurationmessage to the UE, until a particular message is received; and (v)receive a context release message transmitted from the another nodeindicating that the UE has been handed over to a target node.

In another aspect, the invention provides an improved UE. In someembodiments, the improved UE includes: (a) a transmitter fortransmitting data; (b) a receiver for receiving data; and (c) a dataprocessing system operable to (i) establish a connection with a sourcenode; (ii) transmit data units to and receive data units from the sourcenode after establishing the connection; (iii) receive from the sourcenode a reconfiguration message identifying a target node; and (iv)transmit to the target node a message comprising a downlink (DL) countvalue and an uplink (UL) count value in response to receiving thereconfiguration message.

The above and other aspects and embodiments are described below withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention. In the drawings, likereference numbers indicate identical or functionally similar elements.

FIG. 1 illustrates a wireless communication network according to anembodiment of the invention.

FIG. 2 is a flow chart illustrating a process according to someembodiments of the invention.

FIG. 3 illustrates a message flow according to an embodiment of theinvention.

FIG. 4 is a flow chart illustrating a process according to someembodiments of the invention.

FIG. 5 illustrates a message flow according to an embodiment of theinvention.

FIG. 6 is a block diagram that illustrates a node according to anembodiment of the invention.

FIG. 7 is a block diagram that illustrates a UE according to anembodiment of the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, FIG. 1 illustrates a block diagram of a wirelesscommunication network 100. As shown in FIG. 1, the wirelesscommunication network 100 connects a UE 102 with a core network 110 viaa plurality of nodes 104 a, 104 b (e.g., base stations 104 a, 104 b orother access points) connected to an MME 106. As shown in FIG. 1, the UE102 is in wireless communication with a source node 104 a. In someembodiments, the UE 102 can be a cellular telephone handset, asmartphone, a PDA, or other wireless device configured to interoperatewith the wireless network 100. Each of the nodes 104 a, 104 bcommunicates with the MME 106, e.g. for sending and receiving UE dataand for sending and receiving network management messages. In someembodiments, the nodes 104 a, 104 b communicate with the MME 106according to the S1 application protocol. Also as shown in FIG. 1, insome embodiments the nodes 104 a, 104 b may communicate with each other,e.g. for sending and receiving data traffic of the UE 102 and forsending and receiving network management messages. In some embodiments,the nodes 104 a, 104 b communicate with each other according to the X2application protocol.

Referring to FIG. 2, FIG. 2 illustrates an improved handover process 200for transferring the connection for a UE 102 between a source node(e.g., node 104 a) and a target node (e.g., node 104 b) according tosome embodiments of the invention.

In the embodiment shown, the handover process 200 begins at step 202when the source node 104 a transmits an S1AP Handover Required message301 (see FIG. 3, which shows a message flow according to an embodimentof the invention) to the MME 106, indicating that the UE 102 requires ahandover.

In response to receiving the S1AP Handover Required message 301 from thesource node 104 a, at step 204 the MME 106 transmits an S1AP HandoverRequest message 302 to the target node 104 b.

In response to receiving the S1AP Handover Request message 302 from theMME 106, at step 206 the target node 104 b returns an S1AP HandoverRequest Acknowledge message 303 to the MME 106.

After the MME 106 receives the S1AP Handover Request Acknowledge message303 from the target node 104 b, at step 208 the MME 106 transmits anS1AP Handover Command message 304 to source node 104 a.

Upon receiving the S1AP Handover Command message 304 from the MME 106,at step 210 the source node 104 a transmits a Radio Resource Control(“RRC”) Connection Reconfiguration message 305 to the UE 102.

In response to receiving the Connection Reconfiguration message 305 fromthe source node 104 a, the UE 102 performs the reconfigurationsnecessary for executing the handoff. When the reconfigurations arecomplete, at step 212 the UE transmits a Connection ReconfigurationComplete message 306 to the target node 104 b. The ConnectionReconfiguration Complete message 306 includes a DL count value and an ULcount value. In some embodiments, the DL count value includes (1) asequence number and/or (2) a Hyper Frame Number (HFN) that the targetnode should assign to a DL data unit that does not have a sequencenumber assigned to it and that is intended for the UE, and the UL countvalue comprises (1) a sequence number and/or (2) a Hyper Frame Number(HFN). In some embodiments, the Connection Reconfiguration Completemessage 306 comprises at least the information in an RRC ConnectionReconfiguration Complete message, the DL count, and the UL count.

After the target node 104 b receives the Reconfiguration Completemessage 306 from the UE 102, at step 214 the target node beginsscheduling traffic for the UE 102. For example, in some embodiments thetarget node 104 b may allocate resources for the upload and download ofdata between the UE 102 and the external network. Furthermore, at step214 the target node 104 b transmits an S1AP Handover Notify message 307to the MME 106.

In response to receiving the Handover Notify message 307 from the targetnode 104 b indicating that the UE 102 is in communication with thetarget node 104 b, at step 216 the MME 106 transmits an S1AP UE ContextRelease Command message 308 to the source node 104 a indicating that theUE 102 has been handed over to the target node 104 b.

After receiving the Context Release Command message 308, at step 218 thesource node 104 a ceases scheduling traffic for the UE 102 and transmitsan S1AP UE Context Release Complete message 309 to the MME 106.

As set forth above, in some embodiments after the source node 104 atransmits the Connection Reconfiguration message 305, the source node104 a may continue to schedule traffic for the UE 102 until the sourcenode 104 a receives the Context Release Command message 308.

Referring again to FIG. 3, FIG. 3 illustrates a message flow accordingto some embodiments of the invention. As shown in FIG. 3, after thesource node 104 a transmits the Connection Reconfiguration message 305,it forwards UE data 310. In some embodiments, this may comprisecontinuing to deliver to the MME data units received from the UE untilthe Context Release Command message 308 is received. Additionally, thesource node 104 a may continue to assign sequence numbers to DL dataunits intended for the UE and transmit these units to the target node.The target node 104 b determines whether to transmit forwarded packetsto the UE based upon a comparison between the DL count informationreceived in the Connection Reconfiguration Complete message 306 and thesequence numbers of the forwarded packets.

Referring to FIG. 4, FIG. 4 illustrates an improved handover process 400for transferring the connection for a UE 102 between a source node(e.g., node 104 a) and a target node (e.g., node 104 b) according toadditional embodiments of the invention.

The handover process 400 begins at step 402 when the source node 104 atransmits an X2AP Handover Request message 501 (see FIG. 5, which showsa message flow according to an embodiment of the invention) to thetarget node 104 b, indicating that the UE 102 requires a handover.

In response to receiving the Handover Required message 501 from thesource node 104 a, at step 404 the target node 104 b transmits an X2APHandover Request Acknowledge message 503 to the source node 104 a.

Upon receiving the Handover Request Acknowledge message 503 from thetarget node 104 b, at step 406 the source node 104 a transmits a RadioResource Control (“RRC”) Connection Reconfiguration message 505 to theUE 102.

After the source node 104 a transmits the Connection Reconfigurationmessage 505, at step 408 the source node 104 a forwards UE data 510 tothe target node 104 b.

In response to receiving the Connection Reconfiguration message 505 fromthe source node 104 a, the UE 102 performs the reconfigurationsnecessary for executing the handoff. When the reconfigurations arecomplete, at step 410 the UE transmits a Connection ReconfigurationComplete message 506 to the target node 104 b. The ConnectionReconfiguration Complete message 506 includes a DL count value and an ULcount value. In some embodiments, the Connection ReconfigurationComplete message 306 comprises at least the information in a RRCConnection Reconfiguration Complete message, the DL count, and the ULcount.

After the target node 104 b receives the Reconfiguration Completemessage 506 from the UE 102, at step 412 the target node beginsscheduling traffic for the UE 102. For example, in some embodiments thetarget node 104 b may allocate resources for the upload and download ofdata between the UE 102 and the external network. Furthermore, at step412 the target node 104 b transmits an S1AP Path Switch Request message507 a to the MME 106.

In response to receiving the Path Switch Request message 507 a from thetarget node 104 b indicating that the UE 102 is in communication withthe target node 104 b, at step 414 the MME 106 transmits a User PlaneUpdate Request 507 b to the serving gateway (“S-GW”).

At step 416, in response to receiving the User Plane Update Request 507b from the MME 106 the S-GW transmits a User Plane Update Responsemessage 508 a to the MME 106. Additionally in step 416, the S-GWtransmits an end marker 511 to the source node 104 a.

After receiving the end marker 511, at step 418 the source node 104 aceases scheduling traffic for the UE 102. After the source node 104 acompletes this process, it transmits an end marker message 512 to thetarget node 104 b.

In response to receiving the User Plane Update Response message 508 a,at step 420 the MME 106 transmits an S1AP Patch Switch Acknowledgemessage 508 b to the target node 104 b.

After the target node 104 b receives the Patch Switch Acknowledgemessage 508 b, at step 422 the target node 104 b receives additional newUE data from the S-GW and transmits the UE data to the UE 102.

After the above steps have completed, at step 424 the target node 104 btransmits a X2AP UE Context Release message 508 c to the source node 104a.

Referring now to FIG. 6, FIG. 6 is a functional block diagram of a node104 according to some embodiments of the invention. As shown, the node104 may comprise a data processing system 602 (e.g., one or moremicroprocessors), a data storage system 606 (e.g., one or morenon-volatile storage devices) and computer software 608 stored on thestorage system 306. Configuration parameters 610 may also be stored instorage system 606. The node 104 also includes transmit/receive (Tx/Rx)circuitry 604 and 605 for transmitting data to and receiving data fromthe UE 102, and the MME 106, respectively.

The software 608 is configured such that when the processing system 602executes software 608, node 104 performs steps described herein (e.g.,steps described above with reference to the flow chart shown in FIG. 2or 4). For example, the software 608 may include: (1) computerinstructions for transmitting to another node a first handover messagethat indicates that the UE requires a handover; (2) computerinstructions for receiving a second handover message transmitted fromthe another node in response to the first handover message, (3) computerinstructions for transmitting from the source node a reconfigurationmessage to the UE in response to receiving the second handover message;(4) computer instructions for continuing to schedule the UE aftertransmitting the reconfiguration message until a particular message isreceived; and (5) computer instructions for receiving a context releasemessage transmitted from the another node indicating that the UE hasbeen handed over to the target node.

Additionally, the software 608 may include: (1) computer instructionsfor receiving a handover request message transmitted from another node;(2) computer instructions for transmitting to the another node ahandover acknowledge message in response to the handover requestmessage; (3) computer instructions for receiving at the target node amessage transmitted from the UE comprising a DL count value and a ULcount value after transmitting the handover acknowledge message andbefore scheduling the UE in the target node; and (4) using the DL countvalue and/or the UL count value in a communication with the UE afterreceiving the message from the UE.

Referring now to FIG. 7, FIG. 7 is a functional block diagram of a UE102 according to some embodiments of the invention. As shown, the UE 102may comprise a data processing system 702 (e.g., one or moremicroprocessors), a data storage system 706 (e.g., one or morenon-volatile storage devices) and computer software 708 stored on thestorage system 706. Configuration parameters 710 may also be stored instorage system 706. The UE 102 also includes transmit/receive (Tx/Rx)circuitry 704 for transmitting data to and receiving data from node 104,respectively.

The software 708 is configured such that when the processing system 702executes software 708, UE 102 performs steps described herein (e.g.,steps described above with reference to the flow chart shown in FIG. 2or 4). For example, the software 708 may include: (1) computerinstructions for establishing a connection with a source node; (2)computer instructions for transmitting data units to and receiving dataunits from the source node after establishing the connection; (3)computer instructions for receiving from the source node areconfiguration message identifying a target node; and (4) computerinstructions for transmitting to the target node a message comprising aDL count value and an UL count value after receiving the reconfigurationmessage.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above describedexemplary embodiments.

Additionally, while the process described above and illustrated in thedrawings is shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

1. A method for handing over a user equipment (UE) from a source node toa target node, comprising: transmitting from a source node to anothernode a first handover message, wherein the first handover messagerequests handover of a connection associated with a UE; receiving at thesource node a second handover message, wherein the second handovermessage acknowledges receipt of the first handover message; in responseto receiving the second handover message, transmitting from the sourcenode a reconfiguration message to the UE; after transmitting thereconfiguration message from the source node to the UE, continuing toschedule at the source node transmissions for the connection of the UEuntil the source node receives a message of a first message type for theconnection; and upon receiving at the source node the message of thefirst message type for the connection, ceasing to schedule at the sourcenode transmissions for the connection.
 2. The method of claim 1, furthercomprising receiving at the source node a context release messagetransmitted from the another node indicating that the connection for theUE has been handed over to the target node.
 3. The method of claim 1,wherein the another node comprises the target node.
 4. The method ofclaim 3, wherein: the first handover message comprises an X2 ApplicationProtocol (X2AP) Handover Request message; and the second handovermessage comprises an X2AP Handover Request Acknowledge message.
 5. Themethod of claim 4, wherein the message of the first message typecomprises an end marker transmitted from a gateway.
 6. The method ofclaim 1, wherein the another node comprises a mobility management entity(MME).
 7. The method of claim 5, wherein: the first handover messagecomprises an S1 Application protocol (S1AP) Handover Required message;and the second handover message comprises an S1AP Handover Commandmessage.
 8. The method of claim 7, wherein the message of the firstmessage type comprises an S1AP UE Context Release Command message. 9.The method of claim 7, further comprising refraining from transmitting astatus transfer message from the source node to the MME responsive tothe S1AP Handover Command message from the MME.
 10. The method of claim1, further comprising: after transmitting the reconfiguration message tothe UE and before receiving the message of the first message type at thesource node for the connection, transmitting UE data from the sourcenode to the target node, wherein the UE data comprises data receivedfrom the UE or data intended for the UE.
 11. The method of claim 1,further comprising: after transmitting the reconfiguration message fromthe source node to the UE, continuing to (i) assign sequence numbers todownlink (DL) data units intended for the UE and (ii) deliver data unitsreceived from the UE to a core network node until the message of thefirst message type is received at the source node for the connection.12. A method performed by a user equipment (UE), comprising:establishing a connection with a source node; transmitting data units toand receiving data units from the source node using the connection;after establishing the connection, receiving from the source node areconfiguration message identifying a target node; and after receivingthe reconfiguration message, transmitting to the target node a messagecomprising a downlink (DL) count value and an uplink (UL) count valuefor the connection.
 13. The method of claim 12, wherein the messagetransmitted from the UE to the target node comprises a reconfigurationcomplete message.
 14. The method of claim 12, wherein the DL count valuecomprises (1) a sequence number or (2) a Hyper Frame Number (HFN) thatthe target node should assign to a DL data unit intended for the UE thatdoes not have an assigned sequence number; and the UL count valuecomprises (1) a sequence number or (2) a Hyper Frame Number (HFN). 15.The method of claim 12, further comprising: after receiving thereconfiguration message, receiving a resource allocation from the sourcenode; and using the allocated resource to transmit a data unit.
 16. Amethod for handing over a user equipment (UE) from a source node to atarget node, comprising: receiving at a target node a first handovermessage transmitted from another node, the first handover messageindicating a handover has been requested for a connection associatedwith a UE; transmitting to the another node a second handover message,wherein the second handover message acknowledges receipt of the firsthandover message; after transmitting the second handover message andbefore scheduling the UE in the target node, receiving at the targetnode a message transmitted from the UE comprising a DL count value and aUL count value for the connection; and after receiving the message fromthe UE, using the DL count value or the UL count value in transmittingdata to the UE or in receiving data from the UE.
 17. The method of claim16, wherein the message transmitted from the UE is a reconfigurationcomplete message that was transmitted by the UE to the target node inresponse to a reconfiguration message transmitted to the UE from thesource node.
 18. The method of claim 16, wherein the DL count valuecomprises (1) a sequence number or (2) a Hyper Frame Number (HFN) thatthe target node should assign to a DL data unit intended for the UE thatdoes not have an assigned sequence number; and the UL count valuecomprises (1) a sequence number or (2) a Hyper Frame Number (HFN). 19.The method of claim 16, further comprising: receiving from the sourcenode a DL data unit for the UE; and determining whether the DL data unitshould be transmitted to the UE, wherein the determination is based onthe DL count value received from the UE.
 20. An access point,comprising: a first receiver configured to receive data from a userequipment (UE); a first transmitter configured to transmit data to theUE; a second transmitter configured to transmit data to a node; a secondreceiver configured to transmit data to the node; and a data processingsystem configured to: transmit to the node a first handover message,wherein the first handover message requests a handover of a connectionassociated with a UE; receive a second handover message, wherein thesecond handover message acknowledges receipt of the first handovermessage; in response to receiving the second handover message, transmita reconfiguration message to the UE; after transmitting thereconfiguration message to the UE, continue to schedule transmissionsfor the connection of the UE until the source node receives a message ofa first message type for the connection; and upon receiving the messageof the first message type for the connection, ceasing to scheduletransmissions for the connection.
 21. A user equipment (UE), comprising:a transmitter configured to transmit data; a receiver configured toreceive data; and a data processing system configured to: establish aconnection with a source node; transmit data units to and receive dataunits from the source node using the connection; after establishing theconnection, receive from the source node a reconfiguration messageidentifying a target node; and transmit to the target node a messagecomprising a downlink (DL) count value and an uplink (UL) count value inresponse to receiving the reconfiguration message.
 22. An access point,comprising: a first receiver configured to receive data from a userequipment (UE); a first transmitter configured to transmit data to theUE; a second transmitter configured to transmit data to a node; a secondreceiver configured to transmit data to the node; and a data processingsystem configured to: receive a first handover message transmitted fromthe node, the first handover message indicating a handover has beenrequested for a connection associated with the UE; transmit to the nodea second handover message, wherein the second handover messageacknowledges receipt of the first handover message; after transmittingthe second handover message and before scheduling the UE, receive amessage transmitted from the UE comprising a DL count value and a ULcount value for the connection; and after receiving the message from theUE, using the DL count value or the UL count value in transmitting datato the UE or in receiving data from the UE.